Many different kinds of viscous materials are used in the construction industry, including, for example, adhesives and wallboard mud or joint compound. These materials are usually premixed and applied to the work surface using hand tools. The proper application of the materials require a certain degree of skill and technique to consistently obtain high quality finishing results. Variations in composition, texture and viscosity of the materials often lead to inconsistent results even when applied by an experienced worker.
Numerous tools have been developed over the years to increase the speed and ease of applying the viscous materials to the work surface. One form of tool includes a pumping apparatus to deliver the material from a supply container to a dispensing head. These previous pump devices often have difficulty pumping high viscosity materials. A problem commonly encountered with the pumping of high viscosity materials is the surging of the material through the discharge outlet. Surging is particularly great when a change in the output flow rate is needed and the pump attempts to provide an immediate response to the pressure change. Thus, the previous pump operated devices for dispensing and applying viscous construction materials are difficult to use to obtain consistent results.
A major deficiency in the previous pump operated devices is the short operating life of the pump when applying viscous materials containing abrasive fillers or other solids. For example, wallboard joint compound contains large amounts of calcium sulfate dihydrate and silica fillers. These fillers are highly abrasive which quickly erode any wear surfaces in the pump and in particular bearing surfaces and impeller surfaces. The high rate of wear on the impeller surfaces quickly result in a loss of pump pressure thereby rendering the pump unserviceable.
Many adhesive and mastic materials contain volatile or toxic solvents. It is generally desirable to contain the vapors during application of the materials. The prior applicators do not adequately collect volatile and toxic solvents in a suitable containment unit for proper disposal.
Examples of prior devices for applying adhesives, wallboard mud or joint compound and other materials are generally disclosed in U.S. Pat. Nos. 5,013,389 to Retti; 5,240,500 to Retti; 5,279,684 to Retti; 4,477,304 to Westermann; 2,666,323 to Ames; and 3,007,837 to Goode, Jr. These patents have attained only limited success due in part to the inability of the devices to withstand the abrasive nature of many of the compounds being applied. Some of these devices include complex electronic controls to deliver the material at predetermined rates. These electronic controls add considerably to the manufacturing costs and maintenance of the tools, while not solving the problem of lack of uniformly controlled flow of mastic. Thus, there is a continuing need in the industry for a suitable tool for applying viscous materials to a work surface.